Go Ahead, Rationalize. Monkeys Do It, Too.

For half a century, social psychologists have been trying to figure out the human gift for rationalizing irrational behavior. Why did we evolve with brains that salute our shrewdness for buying the neon yellow car with bad gas mileage? The brain keeps sending one message — Yesss! Genius! — while

our friends and family are saying,

“Well... ”

This self-delusion, the result of what’s called cognitive dissonance, has been demonstrated over and over by researchers who have come up with increasingly elaborate explanations for it. Psychologists have suggested we hone our skills of rationalization in order to impress others, reaffirm our “moral integrity” and protect our “self-concept” and feeling of “global self-worth.”

If so, capuchin monkeys are a lot more complicated than we thought. Or, we’re less complicated. In a paper in Psychological Science, researchers at Yale report finding the first evidence of cognitive dissonance in monkeys and in a group in some ways even less sophisticated, 4-year-old humans.

The Yale experiment was a variation of the classic one that first demonstrated cognitive dissonance, a term coined by the social psychologist Leon Festinger. In 1956 one of his students, Jack Brehm, carted some of his own wedding gifts into the lab (it was a low-budget experiment) and asked people to rate the desirability of things like an electric sandwich press, a desk lamp, a stopwatch and a transistor radio.

Then they were given a choice between two items they considered equally attractive, and told they could take one home. (At the end of the experiment Mr. Brehm had to confess he couldn’t really afford to give them anything, causing one woman to break down in tears.) After making a choice (but before having it snatched away), they were asked to rate all the items again.

Suddenly they had a new perspective. If they had chosen the electric sandwich press over the toaster, they raised its rating and downgraded the toaster. They convinced themselves they had made by far the right choice.

So, apparently, did the children and capuchin monkeys studied at Yale by Louisa C. Egan, Laurie R. Santos and Paul Bloom. The psychologists offered the children stickers and the monkeys M&M’s.

Once a monkey was observed to show an equal preference for three colors of M&M’s — say, red, blue and green — he was given a choice between two of them. If he chose red over blue, his preference changed and he downgraded blue. When he was subsequently given a choice between blue and green, it was no longer an even contest — he was now much more likely to reject the blue.

The monkey seemed to be coping the same way humans do. When you reject the toaster, you could spend a lot of time second-guessing yourself, and that phenomenon, much less common, is called buyer’s remorse. (For more on that, go to www.tierneylab.com.)

But in general, people deal with cognitive dissonance — the clashing of conflicting thoughts — by eliminating one of the thoughts. The notion that the toaster is desirable conflicts with the knowledge that you just passed it up, so you banish the notion. The cognitive dissonance is gone; you are smug.

Of course, when you see others engaging in this sort of rationalization, it can look silly or pathological, as if they have a desperate need to justify themselves or are cynically telling lies they couldn’t possibly believe themselves. But you don’t expect to see such high-level mental contortions in 4-year-olds or monkeys.

As the Yale researchers write, these results indicate either that monkeys and children have “richer motivational complexity” than we realize, or our ways of dealing with cognitive dissonance are “mechanistically simpler than previously thought.” Another psychologist, Matthew D. Lieberman of the University of California, Los Angeles, suggests it’s the latter.

“If little children and primates show pretty much the same pattern you see in adults, it calls into question just how deliberate these rationalization processes are,” he says. “We tend to think people have an explicit agenda to rewrite history to make themselves look right, but that’s an outsider’s perspective. This experiment shows that there isn’t always much conscious thought going on.”

The new results jibe with those of a dissonance experiment that Dr. Lieberman and colleagues did with amnesiacs, people with impaired short-term memories, who were asked to rank an assortment of paintings. Then they chose among selected ones and ranked the whole group again. By the second time they ranked the paintings, they couldn’t consciously recall their earlier rankings or their choices, so they presumably didn’t have a psychic need to rewrite history.

Yet they showed as much new disdain for the paintings they’d rejected as did a control group with normal memories. Apparently, the rejections registered in some unconscious way, so that the amnesiacs rationalized their decisions even though they couldn’t remember them.

The compulsion to justify decisions may seem irrational, and maybe petty, too, like the fox in Aesop’s fable who stopped trying for the grapes and promptly told himself they were sour anyway. But perhaps Aesop didn’t appreciate the evolutionary utility of this behavior for humans as well as animals.

Once a decision has been made, second-guessing may just interfere with more important business. A fox who pines for abandoned grapes or a monkey who keeps agonizing over food choices could be wasting energy better expended obtaining the next meal.

And if you are the owner of a yellow gas-guzzler, you might as well convince yourself that the sensible blue car you passed up was an ugly bore. Aesop may call it sour grapes; you can call it moving on. Maybe your unconscious realizes you don’t have time for buyer’s remorse. You’ve got car payments to make.

Correction: November 12, 2007

Illustrations with the Findings column in Science Times on Tuesday, about studies showing cognitive dissonance in monkeys and 4-year-olds, included an unrelated picture. The monkey shown was a macaque monkey, but the research was conducted with capuchins.

A version of this article appears in print on , on page F1 of the New York edition with the headline: Go Ahead, Rationalize. Monkeys Do It, Too. Order Reprints|Today's Paper|Subscribe